Variable mica condenser



Jan. 24, 1933.

MVENTOR Edwawd 06 flown f; 'ERNEY E. J. CQWAN VARIABLE MICA CONDENSERFiled Oct. 24, 1928 Patente Jan. 24, 1933 UNITED STATES PATENT OFFICEEDWARD J. COWAN, F DEDHAM, MASSACHUSETTS, ASSIGNOR, ."BY MESNE ASSIGN-MENIQ, '10 GENERAL ELECTRIC COMPANY,

A CORPORATION OF NEW YORK VARIABLE MICA. CONDENSER.

Application filed October 24, 1928. Serial No. 314,603.

This invention relates to an improved variable condenser of the soliddielectric type which is adapted for use at substantially any frequency.

It is an object of this invention to provide a variable condenser of thesolid dielectric type which 'is characterized by an infinitely finevariation in capacity.

It is a further object of'this invention to provide such an improvedcapacitonwhich is adapted for use in a variety of c1rcu1ts and at anycurrent potential."

Yet another object of this invention 1s the provision of an improvedcapacitor comprising novel elements of design whereby the whole isrendered easy to operateand may be made at a minimum of cost and expensein both labor and materials.

These and other desirable objects of the invention will be described inthe accom panying specification and illustrated in the drawing, certainpreferred embodiments being shown b way of illustratlon only, for sincethe un erlying principles may be embodied in other mechanicalconstructions, it

is not intended to be limited to the ones herein shown except as suchlimitations are clearly imposed by the appended claims.

In the drawing like numerals refer to simito lar parts thruout theseveral views, of WlllCh Fig. 1 is a top plan view of a completedassembly;

Fig. 2 is a rear view of the structure shown in Fig. l; n

Fig. 3 is a vertical section taken on line 33 of Fig. 2, certain partsbeing shown in elevation; and Y Fig. 4 is a cross section of .amodification -of the active elements shown in Fig. 3.

to Referring now to the drawing, there 1s shown a capacitor comprising abase 1 of insulating material such asbakelite, impregnated wood, orother suitable material. This member may have any suitable configurationac- 4 cording to the size of the completed unit.

' The base member 1 is apertured at 2, 3 and 4 to receive securing means5,6 and 7 whose function will be described more in detail hereinafter.

' Superimposed on the base and secured similar in construction to member8 and has thereto by screws 5 and 6 is a fixed capacitor member orstator 8 shown as a block of any metal having the requisite electricalconductivity. This armature is apertured at 9' to receive the threadedterminal 10, which in turn is provided with lock nuts 11, 12 having lockwashers 13 interposed therebetween. The armature 8 is substantiallyprismatic in form, having a bottom 14, vertical sides 15 and back'16,the latter apertured at 9, and an angular face .17. Engaging a slot 18in the base member as a sheet is a dielectric member 19 lying on theangular face 17 of armature 8 and consisting of mica, sulfur, glass orany other suitable material having the desired dielectric constant andelectrical characteristics requisite for a given capacitor. While anumber of materials of different electrical characteristics have beenillustrated above, it will, of course, be understood that any variationin the dielectric constant desired may be secured by varying either thecomposition of the material used, or the thickness of the material.- Itis preferred to use mica of suitable thickness for most purposes, butwhere desired, sulfur may appropriately be used, and its characteristicsmay be varied by incorporating therein a desired percentage of powderedquartz or other like modifying material. This dielectric member 19 maybe secured to the plane inclined face 17 of the stator 8 by any suitablecementing material such as flexible collodi-on or other materials havingthe necessary electrical characteristics and flexible properties. Amovable wedge shaped member 20 of suitable configuration is adapted tomove in sliding contact on dielectric sheet 19, and the capacity betweenit and member 8 is varied by varying the relative areas of inclined face17 of member 8 and inclined face 21 of member 20, which are presented toeach other in cooperative relationship. This armature 20 issubstantially an angular face 21 and side faces 22, back face 23 and topface 24.. The top face 24 is provided with a channeled portion 25 whosefunction will be described more in detail hereinafter. This armature 20is supported and adapted to be moved with respect to member 8 in amanner now to be described.

Mounted on the insulating base 1 is a metallic support 26 comprising aportion 27 adj acent base land angularly disposed with respect toupright portion 28, portion 27 being apertured to receive the bolt andnut construction 7 previously referred to. The upright portion 28 ofthis support 26 is provided with a threaded aperture 29 to receive aknurled micrometer screw 30 the end of which bears against armature 2Otoslide it along inclined dielectric 19. The cooperating threads of theaperture 29 and adjacent member 30 are preferably of the order of 60 to80 threads per inch in order to secure a mic-rometer adjustment of theparts. The support 26 is provided with a top portion 31 bent at rightangles to upright portion. 28 and extending substantially over theentire extent of the upper surface of upper armature 20. Member 31 isapertured at 32 to receive terminal 33,

comprising a shouldered head 34 and a threaded shaft 35. The headedportion 34 is nested in a recess 36 in the lower portion of member 31.Lock nuts 37 and washers 38 are provided to fasten the terminal 33 tothe support 31. Cooperating with the movable armature 20 of thecondenser assembly is the contact shoe 39 adapted for sliding movementin the channel 25 across the top of armature 20. The shoe is providedwith an up standing stud 40 which is adapted to engage a helical spring41, the upper end of which in turn is adapted to nest in the recess 36.The support member 26 is provided further with a pair of laterallydisposed side arms or guard members 42, 43 extending on either side ofarmature 20, and adapted to prevent any lateral movement thereof.

In operation, the micrometer screw 30 is rotated either in or out, asmay be desired, and by its motion causes a relative movement of thearmature 20 on the dielectric 19 supported on the stator armature 8. Thespring 41 by its pressure on shoe 39 tends to keep the movable armature20 pressed downwardly and against adjustment 30 pressing the lowersurface of 20 against the dielectric surface 19 in constant uniformcontact. As above intimated, when the member 30 is moved in or out. thevariable member 30 moves accordingly and more or less of its lowersurface lies opposite the upper surface of armature 8. The channeled topof 20 is adapted to slide along shoe 39, thereby preventing any lateraltranslation of the coil spring member 41. This insures a constantpressure on the movable member 20 by the spring assembly and insuresconstant capacity at any given setting of the micrometer screw 30.

The metal construction of the entire capacitor elements 8 and 20 isperfectly suited for use in ordinary broadcast receiving sets and othercircuits where low frequencies are used, and small voltages areencountered. Where it is desired to use the structure disclosed hereinin high frequency circuits where enormous energy losses may be met withdue to the formation of eddy currents in solid metallic members, thepresent invention comprehends the use of insulating supports or the likebackings for the active metal opposing armature surfaces of members 8and 20, as for example in Fig. 4.

Referring now to Fig. 4, there is shown in vertical cross section a pairof capacitor elements comprising a stator 44 and a movable element 45having a suitable dielectric 46 interposed therebetween. These memberscomprise supporting insulating members 47, 48 of maple wood impregnatedwith wax or the like, or sulfur or other material having the requisitemechanical strength and electrical characteristics at the frequenciesand voltages used. The conducting elements 49, 50 of suitable thicknessand electrical conductivity to handle the currents used, such as thesheets shown, are secured to the faces of the supporting members in anysuitable manner by bending in sheets or in other manners, not shown, theends of these members being separated at 51, 52, 53 and 54 to preventheat losses, due to the short circuited turn effect, which is well knownto those dealing with high frequency currents.

This construction maybe substituted for that in Fig. 3 previouslydescribed, thereby enabling the same device to be used for short wavepurposes without involving any great expense in replacement of theactive units.

It will now be seen that there has been provided an improved variablecapacitor of the solid dielectric type which is characterized by theability to handle all types of currents at various potentials and inwhich a desired capacity regulation is assured by means of a micrometeradjustment.

It will be noted further that due to the s mplicity of the constructionand the cheapness of the materials used, labor and costs for assemblingare appreciably minimized without in any way detracting from the desiredcapacity of the finished unit, as well as its ruggedness and ability tofunction under varying circumstances.

What is claimed is:

.1. A capacitor comprising a sheet of solid dielectric material, a-metalmember on each side of said dielectric, means for making electricalconnections to each of said metal members and means for shifting atleast one of said metal members with respect to the other whichcomprises a support in which said shiftable member is adjustable, ascrew engaging said support for moving said member in one direction, anda spring engaging said support for holding said member against saidscrew, said insulating sheet being disposed atinn angle, and said springand screw being'arranged to act upon one metal member at substantially aright angle to each other, said insulating sheet being disposed at about45 to thedirection in which each of said sprlng and screw acts.

2. A variable capacitor of the solid dielec tric type and including aflat dielectric sheet,

cooperating armatures opposite one another and having fiat facesengaging opposite faces of said dielectric sheet, adjusting means forsliding one of said armatures linearly along the dielectric sheet andvarying the cooperating areas of the opposite armature's; and aspring'holding said movable armature 1n responsive relation to saidadjusting means in various adjusting positions thereof; said spring alsoholding said movable armature in its face-to-face relation with itscooperating armature in various adjusted positions of the movablearmature corresponding to said various adjusting positions of saidadjusting means.

3. A variable capacitor of the solid dielectric type and including aflat dielectric sheet, cooperating armaturesopposite one another andhaving flat faces engaging opposite faces of said dielectric sheet,adjusting means for sliding one of said armatures linearly along thedielectric sheet and varying the cooperatmg armatures being arranged atan angle to the path of adjusting movement of said adjusting means; aspring pressing said movable armature toward both the dielectric sheetand the adjusting means; and means supporting the other armature, theadjusting means and the spring in cooperating relations with the movable armature.

4. A variable capacitor of the solid dielectric type and including aflat dielectric sheet, cooperating armatures opposite one another andhaving fiat faces engaging opposite surfaces of said dielectric sheet;adjusting means for sliding one of said armatures linearly along thedielectric sheet and varying the cooperatlng areas of the oppositearmatures; a spring; and means supporting the other armature, the springand the adjusting means in cooperative relations with the slidablearmature wherein thelatter is held in its various adjusted positions bythe other armature, the

spring and the adjusting means, and where- 111 the spring in saidvarious adjusted positions of the slidable armature presses the lat- Iter in operative engagement with the dielectric sheet and in operativerelation to the ad justing means, and wherein the spring yields to themovement of the slidable armature by the adjusting means whilecontinuing to press the slidable armature against the dielectric sheet,

In testimony whereof 1 hereunto a my signature.

EDWARD J, COMO areas of the opposite armatures; said

